JP2018195509A - Secondary battery electrode covered with polymer layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery electrode coated with a protective layer containing a polymer having excellent ionic conductivity. A secondary battery electrode (4) covered with a polymer layer (3) containing a copolymer of styrene sulfonic acid or a salt thereof and a (meth)acrylic acid-based monomer, wherein styrene sulfonic acid in the polymer layer (3) is used. The secondary battery electrode 4 in which the molar ratio of the monomer unit to the (meth)acrylic acid-based monomer unit is in the range of 9.5:0.5 to 7:3. An electrode 4 for a secondary battery, comprising a current collector 1, a negative electrode active material layer 2 formed on the current collector 1, and a polymer layer 3 that covers the negative electrode active material layer 2 in a double layer. The secondary battery electrode 4 preferably has a structure in which the negative electrode active material layer 2 has a structure in which a plurality of plate-shaped silicon bodies are laminated in the thickness direction. [Selection diagram] Figure 1

Description

  The present invention relates to an electrode for a secondary battery coated with a polymer layer containing a copolymer of styrenesulfonic acid or a salt thereof and a (meth) acrylic acid monomer.

  Secondary batteries typified by lithium ion secondary batteries are currently used mainly as power sources for portable electronic devices, and are also put into practical use as power sources for electric vehicles. Further, a secondary battery having a longer life is required from the industry. Generally, a secondary battery includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and an electrolytic solution. However, the performance of the secondary battery deteriorates as these constituent elements deteriorate.

  As a technique for reducing the direct contact between the positive electrode active material and / or the negative electrode active material and the electrolytic solution in order to prevent deterioration of the positive electrode, the negative electrode, and the electrolytic solution, the surface of the positive electrode active material layer containing the positive electrode active material, the negative electrode A technique for forming a protective layer containing a polymer on the surface of a negative electrode active material layer containing an active material has been proposed.

  For example, Patent Document 1 discloses a technique for coating the surface of a positive electrode active material with a polymer. Specifically, a technique is disclosed in which a positive electrode composed of a current collector and a positive electrode active material layer is immersed in a polyethyleneimine solution and a polyethylene glycol solution, and the positive electrode is coated with a polymer.

  Patent Document 2 also discloses a technique for coating the surface of the positive electrode active material with a polymer. Specifically, a technique is disclosed in which a positive electrode composed of a current collector and a positive electrode active material layer is immersed in a polyethylene glycol solution, and the positive electrode is coated with a polymer.

  Patent Document 3 discloses a technique for strengthening the electrode structure by applying polyethylene oxide to the surface of the active material layer of the electrode, and describes that the capacity retention rate of the secondary battery adopting such a technique has been improved. Has been.

  Patent Document 4 describes an electrode whose surface is coated with poly (meth) acrylic acid. Specific examples thereof include a negative electrode whose surface is coated with polyacrylic acid, and a lithium ion secondary comprising the negative electrode. A battery is described.

JP 2013-243105 A JP 2014-096343 A JP 2013-175477 A Japanese Patent Laid-Open No. 2006-9670

  However, since the polymer is inherently a resistance factor against the movement of charge carriers such as lithium ions, it can be said that the secondary battery to which the technology of the protective layer containing the polymer is applied has a problem in terms of the function as a battery.

  This invention is made | formed in view of this situation, and it aims at providing the electrode for secondary batteries coat | covered with the polymer which is excellent in ion conductivity.

  Now, it is considered that a polymer having excellent ion conductivity needs a moving space surrounded by polar groups for smoothly moving charged ions. Therefore, the present inventor has conceived of using a carboxylic acid group-containing polymer. However, although the material manufactured using polyacrylic acid as a carboxylic acid group-containing polymer was ion-conductive, its degree was low and not always satisfactory.

  The present inventor has studied a material manufactured using a copolymer of acrylic acid and styrene sulfonate as an improvement measure for a material manufactured using polyacrylic acid. The inventors have found that a material using a copolymer having a ratio of acrylic acid to styrene sulfonate within a specific range exhibits ionic conductivity at a satisfactory level. Based on this discovery, the present inventor has completed the present invention.

The electrode for a secondary battery of the present invention is an electrode for a secondary battery coated with a polymer layer containing a copolymer of styrene sulfonic acid or a salt thereof and a (meth) acrylic acid monomer,
The molar ratio of the styrene sulfonic acid monomer unit to the (meth) acrylic acid monomer unit in the polymer layer is in the range of 9.5: 0.5 to 7: 3.

  The secondary battery electrode of the present invention is a secondary battery electrode coated with a new protective layer, whereby a long-life secondary battery can be provided.

It is a cross-sectional schematic diagram which shows the one aspect | mode of the electrode for secondary batteries of this invention.

  Below, the form for implementing this invention is demonstrated. Unless otherwise specified, the numerical range “ab” described herein includes the lower limit “a” and the upper limit “b”. The numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples. Furthermore, numerical values arbitrarily selected from these numerical ranges can be used as new upper and lower numerical values.

An electrode for a secondary battery according to the present invention is an electrode for a secondary battery coated with a polymer layer containing a copolymer of styrene sulfonic acid or a salt thereof and a (meth) acrylic acid monomer, the polymer layer The molar ratio of the styrene sulfonic acid monomer unit to the (meth) acrylic acid monomer unit is in the range of 9.5: 0.5 to 7: 3.
Hereinafter, a copolymer of styrene sulfonic acid or a salt thereof and a (meth) acrylic acid monomer is included, and the molar ratio of the styrene sulfonic acid monomer unit to the (meth) acrylic acid monomer unit is 9.5: 0.5. The polymer layer in the range of ˜7: 3 may be referred to as “polymer layer of the present invention”. In addition, a copolymer of styrene sulfonic acid or a salt thereof and a (meth) acrylic acid monomer may be simply referred to as “copolymer”.

  Examples of the styrene sulfonic acid salt include alkali metal salts such as lithium salt, sodium salt and potassium salt, alkaline earth metal salts such as magnesium salt and calcium salt, and ammonium salt.

  Specific examples of (meth) acrylic acid monomers include (meth) acrylic acid, (meth) acrylate, (meth) acrylonitrile, (meth) acrylamide and (meth) acrylic acid esters, and derivatives thereof. it can. In the present specification, (meth) acrylic acid means acrylic acid, methacrylic acid, or both acrylic acid and methacrylic acid. The same applies to (meth) acrylate, (meth) acrylonitrile, (meth) acrylamide and (meth) acrylic acid ester.

  Examples of the salt of (meth) acrylate include alkali metal salts such as lithium salt, sodium salt and potassium salt, alkaline earth metal salts such as magnesium salt and calcium salt, and ammonium salt. Moreover, as an alcohol site | part of (meth) acrylic acid ester, a C1-C6 alkyl group and a C1-C6 alkyl group which has a substituent can be illustrated. Examples of the alkyl group having 1 to 6 carbon atoms include methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, s-butyl group, i-butyl group, and t-butyl group. A derivative means what has a certain substituent with respect to basic skeletons, such as (meth) acrylic acid, (meth) acrylate, (meth) acrylonitrile, (meth) acrylamide and (meth) acrylate.

  Examples of the substituent in the present specification include an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an unsaturated cycloalkyl group, an aromatic group, a heterocyclic group, a halogen, OH, SH, CN, a nitro group, an alkoxy group, Unsaturated alkoxy group, amino group, alkylamino group, dialkylamino group, aryloxy group, acyl group, alkoxycarbonyl group, acyloxy group, aryloxycarbonyl group, acylamino group, alkoxycarbonylamino group, aryloxycarbonylamino group, sulfonyl Amino group, sulfamoyl group, carbamoyl group, alkylthio group, arylthio group, sulfonyl group, sulfinyl group and the like can be mentioned. These substituents may be further substituted. When there are two or more substituents, the substituents may be the same or different.

  The polymer layer of the present invention is characterized in that the molar ratio of the styrene sulfonic acid monomer unit to the (meth) acrylic acid monomer unit is in the range of 9.5: 0.5 to 7: 3. When the molar ratio is in the range of 9.5: 0.5 to 7: 3, the polymer layer of the present invention exhibits suitable ionic conductivity, and the secondary battery is coated with the polymer layer of the present invention. The working electrode exhibits suitable characteristics. In the polymer layer having a molar ratio outside the range of 9.5: 0.5 to 7: 3, the ionic conductivity is low, and the secondary battery electrode coated with such a polymer layer partially exhibits suitable characteristics. Some exist, but the overall characteristics are not satisfactory.

  The molar ratio of the styrene sulfonic acid monomer unit to the (meth) acrylic acid monomer unit in the polymer layer of the present invention is preferably in the range of 9.5: 0.5 to 7.5: 2.5. The range of 5: 0.5 to 8: 2 is more preferable, and the range of 9.5: 0.5 to 8.5: 1.5 is more preferable. The styrene sulfonic acid monomer unit in the copolymer may contain only a single structure derived from styrene sulfonic acid or a salt thereof, or may contain a plurality of structures. Similarly, the (meth) acrylic acid monomer unit in the copolymer may include only a single structure derived from the (meth) acrylic acid monomer, or may include a plurality of structures.

  A copolymer of styrene sulfonic acid or a salt thereof and a (meth) acrylic acid monomer may be produced under normal polymerization conditions. Specifically, a known catalyst and / or polymerization initiator is added in the presence of styrene sulfonic acid or a salt thereof, a (meth) acrylic acid monomer, and a solvent for dissolving them, and a copolymerization reaction is performed. Just start. In the case of using a photopolymerization initiator or a thermal polymerization initiator, the corresponding light or heat may be supplied to start the copolymerization reaction. The copolymerization reaction is preferably performed in the presence of an inert gas such as nitrogen, argon or helium, and is preferably performed under appropriate temperature control conditions.

  There is no restriction | limiting in particular in the average molecular weight of the copolymer of a styrenesulfonic acid or its salt, and a (meth) acrylic-acid type monomer. As a weight average molecular weight of a copolymer, the range of 5000-4 million, 10000-2000000, 20000-1000000, 500,000-500000 can be illustrated.

  In the polymer layer of the present invention, additives such as known polymers can be blended without departing from the spirit of the present invention. The polymer layer of the present invention preferably contains a copolymer at 50% by mass or more, more preferably contains a copolymer at 70% by mass or more, and more preferably contains a copolymer at 90% by mass or more. . Examples of the polymer layer of the present invention include those composed only of a copolymer.

  The secondary battery electrode of the present invention may be a positive electrode or a negative electrode. The secondary battery of the present invention comprises the secondary battery electrode of the present invention. In the secondary battery of the present invention, both the positive electrode and the negative electrode may be the electrode for the secondary battery of the present invention, and either one of the electrodes is the electrode for the secondary battery of the present invention, and the other is the book. It may be a general electrode not having the polymer layer of the invention.

  Hereinafter, the secondary battery of the present invention including the electrode for the secondary battery of the present invention and the electrode for the secondary battery of the present invention will be described through the description of the lithium ion secondary battery which is a representative example of the secondary battery. . A specific embodiment of the electrode for a secondary battery of the present invention includes a current collector, an active material layer formed on the surface of the current collector, and a polymer layer of the present invention formed on the surface of the active material layer. It is the structure which comprises.

  A current collector refers to a chemically inert electronic conductor that keeps current flowing through an electrode during discharge or charging of a secondary battery such as a lithium ion secondary battery. The material of the current collector is not particularly limited as long as it is a metal that can withstand a voltage suitable for the active material to be used. The current collector material is at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel Examples of such a metal material can be given. The current collector may be covered with a known protective layer. What collected the surface of the electrical power collector by the well-known method may be used as an electrical power collector.

  When the potential of the positive electrode is 4 V or more on the basis of lithium, it is preferable to employ aluminum as the positive electrode current collector.

  Specifically, it is preferable to use a positive electrode current collector made of aluminum or an aluminum alloy. Here, aluminum refers to pure aluminum, and aluminum having a purity of 99.0% or more is referred to as pure aluminum. An alloy obtained by adding various elements to pure aluminum is referred to as an aluminum alloy. Examples of the aluminum alloy include Al—Cu, Al—Mn, Al—Fe, Al—Si, Al—Mg, Al—Mg—Si, and Al—Zn—Mg.

  Specific examples of aluminum or aluminum alloy include A1000 series alloys (pure aluminum series) such as JIS A1085 and A1N30, A3000 series alloys (Al-Mn series) such as JIS A3003 and A3004, JIS A8079, A8021, etc. A8000-based alloy (Al-Fe-based).

  The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 1 μm to 100 μm.

  The active material layer includes an active material that can occlude and release charge carriers such as lithium ions, and a binder and a conductive aid as necessary. The active material layer preferably contains the active material in an amount of 60 to 99% by mass, more preferably 70 to 95% by mass with respect to the mass of the entire active material layer.

As the positive electrode active material, the general formula of the layered rock salt _{structure: Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 2, b + c + d + e = 1,0 ≦ e <1, D is W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, Ti, La, Zr, Cu, Ca, Ir, Hf, Rh, Fe, Ge, Zn, Ru, At least one element selected from Sc, Sn, In, Y, Bi, S, Si, Na, K, P, and V, a lithium mixed metal oxide represented by 1.7 ≦ f ≦ 3), Li ₂ MnO ₃ can be mentioned. Further, as a positive electrode active material, a spinel structure metal oxide such as LiMn ₂ O ₄ , a solid solution composed of a mixture of a spinel structure metal oxide and a layered compound, LiMPO ₄ , LiMVO ₄ or Li ₂ MSiO ₄ (wherein M is selected from at least one of Co, Ni, Mn, and Fe). Furthermore, as the positive electrode active material, tavorite compound (the M a transition metal) LiMPO ₄ F, such as LiFePO ₄ F represented by, Limbo ₃ such LiFeBO ₃ (M is a transition metal) include borate-based compound represented by be able to. Any metal oxide used as the positive electrode active material may have the above composition formula as a basic composition, and a metal element contained in the basic composition may be substituted with another metal element. Moreover, you may use as a positive electrode active material the thing which does not contain a charge carrier (for example, lithium ion which contributes to charging / discharging). For example, sulfur alone, compounds in which sulfur and carbon are compounded, metal sulfides such as TiS ₂ , oxides such as V ₂ O ₅ and MnO ₂ , compounds containing polyaniline and anthraquinone, and aromatics in their chemical structures, conjugated two Conjugated materials such as acetic acid organic materials and other known materials can also be used. Further, a compound having a stable radical such as nitroxide, nitronyl nitroxide, galvinoxyl, phenoxyl, etc. may be adopted as the positive electrode active material. When using a positive electrode active material that does not contain a charge carrier such as lithium, it is necessary to add a charge carrier to the positive electrode and / or the negative electrode in advance by a known method. The charge carrier may be added in an ionic state or in a non-ionic state such as a metal. For example, when the charge carrier is lithium, it may be integrated by attaching a lithium foil to the positive electrode and / or the negative electrode.

From the viewpoint of excellent and high capacity, and durability, as the positive electrode active material, the general formula of the layered rock salt _{structure: Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 2, b + c + d + e = 1,0 ≦ e <1, D is W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, Ti, La, Zr, Cu, Ca, Ir, Hf, At least one element selected from Rh, Fe, Ge, Zn, Ru, Sc, Sn, In, Y, Bi, S, Si, Na, K, P, V, 1.7 ≦ f ≦ 3) It is preferable to employ a lithium composite metal oxide.

  In the above general formula, the values of b, c, and d are not particularly limited as long as the above conditions are satisfied, but those in which 0 <b <1, 0 <c <1, 0 <d <1 are satisfied. And at least one of b, c, and d is in the range of 10/100 <b <90/100, 10/100 <c <90/100, 5/100 <d <70/100. More preferably, the ranges are 20/100 <b <80/100, 12/100 <c <70/100, 10/100 <d <60/100, 30/100 <b <70/100, More preferably, the ranges are 15/100 <c <50/100 and 12/100 <d <50/100.

  About a, e, and f, what is necessary is just a numerical value within the range prescribed | regulated by the said general formula, Preferably 0.5 <= a <= 1.5, 0 <= e <0.2, 1.8 <= f <= 2 0.5, more preferably 0.8 ≦ a ≦ 1.3, 0 ≦ e <0.1, 1.9 ≦ f ≦ 2.1, respectively.

From the viewpoint of excellent and high capacity, and durability, as a positive electrode active material, the _{Li x Mn 2-y A y} O 4 (A spinel structure, Ca, Mg, S, Si , Na, K, Al, P, Ga And at least one element selected from Ge and at least one metal element selected from transition metal elements such as Ni. 0 <x ≦ 2.2, 0 ≦ y ≦ 1). Examples of the value range of x include 0.5 ≦ x ≦ 1.8, 0.7 ≦ x ≦ 1.5, and 0.9 ≦ x ≦ 1.2. The value range of y is 0 ≦ y ≦ 0.8, 0 ≦ y ≦ 0.6 can be exemplified. Specific examples of the spinel structure compound include LiMn ₂ O ₄ and LiMn _1.5 Ni _0.5 O ₄ .

Specific examples of the positive electrode active material include LiFePO ₄ , Li ₂ FeSiO ₄ , LiCoPO ₄ , Li ₂ CoPO ₄ , Li ₂ MnPO ₄ , Li ₂ MnSiO ₄ , and Li ₂ CoPO ₄ F. As another specific positive electrode active material, Li ₂ MnO ₃ —LiCoO ₂ can be exemplified.

As the negative electrode active material, a material that can occlude and release charge carriers can be used. Therefore, there is no particular limitation as long as it is a simple substance, alloy, or compound that can occlude and release charge carriers such as lithium ions. For example, as a negative electrode active material, Li, group 14 elements such as carbon, silicon, germanium and tin, group 13 elements such as aluminum and indium, group 12 elements such as zinc and cadmium, group 15 elements such as antimony and bismuth, magnesium , Alkaline earth metals such as calcium, and group 11 elements such as silver and gold may be employed alone. Specific examples of the alloy or compound include tin-based materials such as Ag-Sn alloy, Cu-Sn alloy, Co-Sn alloy, carbon-based materials such as various graphites, SiO _x (disproportionated to silicon simple substance and silicon dioxide). Examples thereof include silicon-based materials such as 0.3 ≦ x ≦ 1.6), silicon alone, or composites obtained by combining silicon-based materials and carbon-based materials. In addition, as the negative electrode active material, oxides such as Nb ₂ O ₅ , TiO ₂ , Li ₄ Ti ₅ O ₁₂ , WO ₂ , MoO ₂ , Fe ₂ O ₃ , or Li _3-x M _x N (M = A nitride represented by (Co, Ni, Cu) may be employed. One or more of these materials can be used as the negative electrode active material.

  In view of the possibility of increasing the capacity, preferable negative electrode active materials include graphite, Si-containing materials, and Sn-containing materials.

Specific examples of the Si-containing material include Si alone and SiO _x (0.3 ≦ x ≦ 1.6) disproportionated into two phases of a Si phase and a silicon oxide phase. The Si phase in SiO _x can occlude and release lithium ions, and changes in volume as the secondary battery is charged and discharged. The silicon oxide phase has less volume change associated with charge / discharge than the Si phase. That is, SiO _x as the negative electrode active material realizes a high capacity by the Si phase and suppresses the volume change of the entire negative electrode active material by having the silicon oxide phase. If x is less than the lower limit value, the Si ratio becomes excessive, so that the volume change during charging and discharging becomes too large, and the cycle characteristics of the secondary battery deteriorate. On the other hand, when x exceeds the upper limit value, the Si ratio becomes too small and the energy density decreases. The range of x is more preferably 0.5 ≦ x ≦ 1.5, and further preferably 0.7 ≦ x ≦ 1.2.

In the SiO _x as described above, it is believed to alloying reaction with the silicon lithium and Si phase during charging and discharging of the lithium ion secondary battery may occur. And it is thought that this alloying reaction contributes to charging / discharging of a lithium ion secondary battery. Similarly, it is considered that the Sn-containing material described later can be charged and discharged by an alloying reaction between tin and lithium.

Specific examples of the Sn-containing material include Sn alone, tin alloys such as Cu—Sn and Co—Sn, amorphous tin oxide, and tin silicon oxide. SnB _0.4 P _0.6 O _3.1 can be exemplified as the amorphous tin oxide, and SnSiO ₃ can be exemplified as the tin silicon oxide.

  The Si-containing material and the Sn-containing material are preferably combined with a carbon material to form a negative electrode active material. Due to the composite, the structure of silicon and / or tin is particularly stabilized, and the durability of the negative electrode is improved. The above compounding may be performed by a known method. As the carbon material used for the composite, graphite, hard carbon, soft carbon or the like may be employed. The graphite may be natural graphite or artificial graphite.

  Specific examples of the Si-containing material include a silicon material disclosed in International Publication No. 2014/080608 (hereinafter simply referred to as “silicon material”).

The silicon material has a structure in which a plurality of plate-like silicon bodies are laminated in the thickness direction. For example, the silicon material is subjected to a process of synthesizing a layered silicon compound containing polysilane as a main component by reacting CaSi ₂ with an acid, and further a process of heating the layered silicon compound at 300 ° C. or higher to desorb hydrogen. It is manufactured.

The production method of the silicon material is represented by the following ideal reaction formula when hydrogen chloride is used as the acid.
3CaSi ₂ + 6HCl → Si ₆ H ₆ + 3CaCl ₂
Si ₆ H ₆ → 6Si + 3H ₂ ↑

However, in the upper reaction for synthesizing Si ₆ H ₆ which is polysilane, water is usually used as a reaction solvent from the viewpoint of removing by-products and impurities. Since Si ₆ H ₆ can react with water, in the step of synthesizing the layered silicon compound including the upper reaction, the layered silicon compound is hardly manufactured as containing only Si ₆ H ₆ , and the layered The silicon compound is represented by Si ₆ H _s (OH) _t X _u (X is an element or group derived from an acid anion, s + t + u = 6, 0 <s <6, 0 <t <6, 0 <u <6). Manufactured as a product. In the above chemical formula, inevitable impurities such as Ca that can remain are not taken into consideration. A silicon material obtained by heating the layered silicon compound also contains an element derived from an anion of oxygen or acid.

As described above, the silicon material has a structure in which a plurality of plate-like silicon bodies are laminated in the thickness direction. In order to efficiently store and release charge carriers such as lithium ions, the plate-like silicon body preferably has a thickness in the range of 10 nm to 100 nm, more preferably in the range of 20 nm to 50 nm. The length in the longitudinal direction of the plate-like silicon body is preferably within a range of 0.1 μm to 50 μm. The plate-like silicon body preferably has (length in the longitudinal direction) / (thickness) in the range of 2 to 1000. The laminated structure of the plate-like silicon body can be confirmed by observation with a scanning electron microscope or the like. This laminated structure is considered to be a remnant of the Si layer in the raw material CaSi ₂ .

  The silicon material preferably includes amorphous silicon and / or silicon crystallites. In particular, the above plate-like silicon body is preferably in a state where amorphous silicon is used as a matrix and silicon crystallites are scattered in the matrix. The size of the silicon crystallite is preferably in the range of 0.5 nm to 300 nm, more preferably in the range of 1 nm to 100 nm, still more preferably in the range of 1 nm to 50 nm, and particularly preferably in the range of 1 nm to 10 nm. The size of the silicon crystallite is calculated from the Scherrer equation using X-ray diffraction measurement on the silicon material and using the half-value width of the diffraction peak of the Si (111) plane of the obtained X-ray diffraction chart. .

  The abundance and size of the plate-like silicon body, amorphous silicon and silicon crystallite contained in the silicon material mainly depend on the heating temperature and the heating time. The heating temperature is preferably in the range of 350 ° C to 950 ° C, more preferably in the range of 400 ° C to 900 ° C.

  The silicon material may be coated with carbon. A silicon material coated with carbon is excellent in conductivity.

  The average particle size of the silicon material is preferably in the range of 2 to 7 μm, and more preferably in the range of 2.5 to 6.5 μm. If a silicon material having an average particle size that is too small is used, it may be difficult to manufacture the negative electrode from the viewpoint of cohesion and wettability. Specifically, in the slurry prepared at the time of manufacturing the negative electrode, a silicon material having an average particle size that is too small may aggregate. On the other hand, a lithium ion secondary battery including a negative electrode using a silicon material having an excessively large average particle size may not be able to be charged / discharged appropriately. In the case of a silicon material having an average particle size that is too large, it is presumed that lithium ions cannot sufficiently diffuse into the silicon material. In addition, the average particle diameter in this specification means D50 when a sample is measured with a general laser diffraction type particle size distribution measuring apparatus.

  Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, and carboxymethylcellulose. What is necessary is just to employ | adopt well-known things, such as a styrene butadiene rubber.

  A cross-linked polymer obtained by cross-linking a carboxyl group-containing polymer such as polyacrylic acid or polymethacrylic acid with a polyamine such as diamine disclosed in International Publication No. 2016/063882 may be used as a binder.

  Examples of the diamine used in the crosslinked polymer include alkylene diamines such as ethylene diamine, propylene diamine, and hexamethylene diamine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, isophorone diamine, and bis (4-aminocyclohexyl) methane. Saturated carbocyclic diamine, m-phenylenediamine, p-phenylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, bis (4-aminophenyl) sulfone, benzidine, o-tolidine, 2,4- Aromatic diamines such as tolylenediamine, 2,6-tolylenediamine, xylylenediamine, and naphthalenediamine are exemplified.

  The blending ratio of the binder in the active material layer is preferably a mass ratio of active material: binder = 1: 0.005 to 1: 0.3. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.

  The conductive assistant is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be added arbitrarily when the electrode conductivity is insufficient, and may not be added when the electrode conductivity is sufficiently excellent. The conductive auxiliary agent may be any chemically inert electronic high conductor, and examples thereof include carbon black, graphite, Vapor Grown Carbon Fiber, and various metal particles. The Examples of carbon black include acetylene black, ketjen black (registered trademark), furnace black, and channel black. These conductive assistants can be added to the active material layer alone or in combination of two or more. The blending ratio of the conductive assistant in the active material layer is preferably a mass ratio of active material: conductive assistant = 1: 0.01 to 1: 0.5. This is because if the amount of the conductive auxiliary is too small, an efficient conductive path cannot be formed, and if the amount of the conductive auxiliary is too large, the moldability of the active material layer is deteriorated and the energy density of the electrode is lowered.

  In order to form an active material layer on the surface of the current collector, a current collecting method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method can be used. An active material may be applied to the surface of the body. Specifically, an active material, a binder, a solvent, and a conductive additive as necessary are mixed to form a slurry, and the slurry is applied to the surface of the current collector and then dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. In order to increase the electrode density, the dried product may be compressed.

  The electrode for a secondary battery of the present invention is coated with the polymer layer of the present invention. Therefore, it can suppress that the positive electrode active material layer containing a positive electrode active material and / or the negative electrode active material layer containing a negative electrode active material contact with electrolyte solution directly. In addition, since the polymer layer of the present invention has a certain degree of flexibility, it can follow the expansion and contraction of the positive electrode active material and the negative electrode active material accompanying charge / discharge, and the positive electrode active material and the negative electrode active material electrode Can be prevented from falling off.

  Although there is no restriction | limiting in particular in the thickness of the polymer layer of this invention, 0.05-20 micrometers is preferable, 0.1-15 micrometers is more preferable, 0.5-10 micrometers is further more preferable, 0.5-5 micrometers is especially preferable.

  In order to provide the polymer layer of the present invention on the surface of the active material layer, for example, a reaction solution in which a copolymer was produced was appropriately adjusted to an appropriate concentration, and an application step of applying to the surface of the active material layer was performed. Thereafter, a drying process may be performed. Or after isolating a copolymer from the reaction liquid which manufactured the copolymer, the solution which melt | dissolved the isolated copolymer in a solvent may be prepared, and the polymer layer of this invention may be provided. In the coating process, a conventionally known method such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method may be used. The drying step may be performed under normal pressure conditions or under reduced pressure conditions using a vacuum dryer. What is necessary is just to set a drying temperature suitably within the range which a copolymer does not decompose | disassemble, and the temperature beyond the boiling point of a solvent is preferable. What is necessary is just to set drying time suitably according to an application quantity and drying temperature.

  FIG. 1 is a schematic cross-sectional view showing one embodiment of the electrode for a secondary battery of the present invention. The current collector 1 is made of an electron conductor. An active material layer 2 having an active material and a binder is formed on the surface of the current collector 1, and a polymer layer 3 that covers the surface of the active material layer 2 is further formed. The secondary battery electrode 4 includes a current collector 1, an active material layer 2, and a polymer layer 3.

  Specific configurations other than the electrodes in the lithium ion secondary battery of the present invention include a separator and an electrolytic solution.

  The separator separates the positive electrode and the negative electrode and allows lithium ions to pass while preventing a short circuit due to contact between the two electrodes. A known separator may be employed, such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polyamide), polyester, polyacrylonitrile or other synthetic resin, cellulose, amylose or other polysaccharide, fibroin. And porous materials, nonwoven fabrics, woven fabrics, and the like using one or more electrical insulating materials such as natural polymers such as keratin, lignin, and suberin, and ceramics. The separator may have a multilayer structure.

  The electrolytic solution includes a nonaqueous solvent and an electrolyte dissolved in the nonaqueous solvent.

  As the non-aqueous solvent, cyclic esters, chain esters, ethers and the like can be used. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, ethyl methyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. As the non-aqueous solvent, a compound in which part or all of hydrogen in the chemical structure of the specific solvent is substituted with fluorine may be employed.

Examples of the electrolyte include lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ .

As an electrolytic solution, 0.5 mol / liter of a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3 is} added to a non-aqueous solvent such as fluoroethylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. A solution dissolved at a concentration of about 1.7 mol / L from L can be exemplified.

A specific method for producing the lithium ion secondary battery of the present invention will be described.
For example, a separator is sandwiched between a positive electrode and a negative electrode to form an electrode body. The electrode body may be any of a stacked type in which a positive electrode, a separator and a negative electrode are stacked, or a wound type in which a positive electrode, a separator and a negative electrode are stacked. After connecting the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal connected to the outside using a current collecting lead or the like, an electrolyte is added to the electrode body to form a lithium ion secondary battery. Good.

  The shape of the lithium ion secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape can be adopted.

  The lithium ion secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy generated by a lithium ion secondary battery for all or a part of its power source. For example, the vehicle may be an electric vehicle or a hybrid vehicle. When a lithium ion secondary battery is mounted on a vehicle, a plurality of lithium ion secondary batteries may be connected in series to form an assembled battery. Examples of devices equipped with lithium ion secondary batteries include various home appliances driven by batteries such as personal computers and portable communication devices, office devices, and industrial devices in addition to vehicles. Furthermore, the lithium ion secondary battery of the present invention includes wind power generation, solar power generation, hydroelectric power generation and other power system power storage devices and power smoothing devices, power supplies for ships and / or auxiliary power supply sources, aircraft, Power supply for spacecraft and / or auxiliary equipment, auxiliary power supply for vehicles that do not use electricity as a power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, You may use for the electrical storage apparatus which stores temporarily the electric power required for charge in the charging station for electric vehicles.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In addition, this invention is not limited by these Examples.

Example 1
6 g (29.1 mmol) of sodium styrenesulfonate and 0.233 g (3.2 mmol) of acrylic acid were dissolved in 30 g of water to obtain an aqueous solution. Under a nitrogen atmosphere, 30 mg of ammonium persulfate was added to the aqueous solution, and then the temperature of the aqueous solution was heated to 60 ° C. under stirring conditions to initiate the copolymerization reaction. After stirring the reaction solution at 60 ° C. for 5 hours, the reaction solution is cooled to room temperature, and the molar ratio of styrene sulfonic acid monomer units to acrylic acid monomer units is 9: 1. Manufactured.

  The copolymer solution of Example 1 was applied to the surface of an aluminum foil in a film shape, and then heated to remove water, whereby a film-shaped polymer layer of Example 1 was produced.

  Moreover, the negative electrode and lithium ion secondary battery of Example 1 were manufactured as follows using the copolymer solution of Example 1.

CaSi ₂ was added to a concentrated hydrochloric acid solution at 0 ° C. under stirring conditions and reacted for 1 hour. Water was added to the reaction solution, filtration was performed, and a yellow powder was collected by filtration. The yellow powder was washed with water, further washed with ethanol, and then dried under reduced pressure to obtain a layered silicon compound containing layered polysilane. Next, the layered silicon compound was heated at 500 ° C. in an argon atmosphere to release hydrogen to produce a silicon material. A carbon-coated silicon material was manufactured by heating the silicon material at 880 ° C. in a propane gas atmosphere.

  Polyacrylic acid (weight average molecular weight 250,000, Wako Pure Chemical Industries, Ltd.) was dissolved in N-methyl-2-pyrrolidone to produce a polyacrylic acid solution containing 15% by mass of polyacrylic acid. Further, 4,4′-diaminodiphenylmethane (Tokyo Chemical Industry Co., Ltd.) is dissolved in N-methyl-2-pyrrolidone, and 4,4′-diaminomethane containing 50% by mass of 4,4′-diaminodiphenylmethane is contained. A diphenylmethane solution was prepared. Under a nitrogen atmosphere, a mixture of 12.7 parts by mass of the polyacrylic acid solution and 1.05 parts by mass of the 4,4′-diaminodiphenylmethane solution was stirred at room temperature for 30 minutes, and further stirred at 110 ° C. for 2 hours. A binder solution was produced.

  72.5 parts by mass of a carbon-coated silicon material as a negative electrode active material, 13.5 parts by mass of acetylene black as a conductive additive, and the above binder solution in an amount of 14 parts by mass as a binder, and an appropriate amount N-methyl-2-pyrrolidone was mixed to produce a slurry. A copper foil having a thickness of 30 μm was prepared as a negative electrode current collector. The slurry was applied in a film form on the surface of the copper foil using a doctor blade. The copper foil coated with the slurry was dried to remove N-methyl-2-pyrrolidone. Thereafter, the copper foil was pressed to obtain a bonded product. The obtained joined product was heat-dried at 180 ° C. for 2 hours with a vacuum dryer to produce a negative electrode precursor on which a negative active material layer having a thickness of 20 μm was formed. The mixture of polyacrylic acid and 4,4′-diaminodiphenylmethane used as the binder was subjected to a dehydration reaction by the above-mentioned heat drying, and the polyacrylic acid was crosslinked with 4,4′-diaminodiphenylmethane. Change to cross-linked polymer.

  The copolymer solution of Example 1 was applied to the surface of the negative electrode precursor in the form of a film, and then heated to remove water, thereby providing a negative electrode active material layer coated with a polymer layer having a thickness of several μm. The negative electrode of Example 1 was manufactured.

The negative electrode of Example 1 was cut into a diameter of 11 mm to obtain an evaluation electrode. A metal lithium foil having a thickness of 500 μm was cut into a diameter of 16 mm to obtain a counter electrode. As a separator, a glass filter (Hoechst Celanese) and celgard 2400 (Polypore Corporation), which is a single-layer polypropylene, were prepared. It was also prepared an electrolyte solution obtained by dissolving LiPF ₆ at 1 mol / L in a solvent obtained by mixing 50 parts by volume of ethylene carbonate and diethyl carbonate 50 parts by volume. Two kinds of separators were sandwiched between the counter electrode and the evaluation electrode in the order of the counter electrode, the glass filter, celgard 2400, and the evaluation electrode, thereby forming an electrode body. This electrode body was accommodated in a coin-type battery case CR2032 (Hosen Co., Ltd.), and an electrolyte was further injected to obtain a coin-type battery. This was designated as the lithium ion secondary battery of Example 1.

(Example 2)
A copolymer solution, a polymer layer, a negative electrode, and a lithium ion secondary battery of Example 2 were produced in the same manner as in Example 1 except that 0.526 g (7.3 mmol) of acrylic acid was used. In the copolymer solution of Example 2, the molar ratio of the styrene sulfonic acid monomer unit to the acrylic acid monomer unit is 8: 2.

Example 3
A copolymer solution, a polymer layer, a negative electrode, and a lithium ion secondary battery of Example 3 were produced in the same manner as in Example 1 except that 0.899 g (12.5 mmol) of acrylic acid was used. In the copolymer solution of Example 3, the molar ratio of the styrene sulfonic acid monomer unit to the acrylic acid monomer unit is 7: 3.

(Comparative Example 1)
6.67 g (32.2 mmol) of sodium styrenesulfonate was dissolved in 30 g of water to obtain an aqueous solution. Under a nitrogen atmosphere, 30 mg of ammonium persulfate was added to the aqueous solution, and then the temperature of the aqueous solution was heated to 60 ° C. under stirring conditions to initiate the polymerization reaction. Hereinafter, the polymer solution, polymer layer, negative electrode, and lithium ion secondary battery of Comparative Example 1 were produced in the same manner as in Example 1. In the polymer solution of Comparative Example 1, the molar ratio of the styrene sulfonic acid monomer unit to the acrylic acid monomer unit is 10: 0.
In addition, when an attempt was made to produce the polymer layer of Comparative Example 1 from the polymer solution of Comparative Example 1 in the same manner as in Example 1, the polymer solution gradually became cloudy with the removal of water, and finally A polymer in powder form was produced. The polymer in the powder state was subjected to the following evaluation as a polymer layer of Comparative Example 1.

(Comparative Example 2)
The copolymer solution, polymer layer, negative electrode and comparative example 2 were prepared in the same manner as in Example 1 except that 3 g (14.6 mmol) of sodium styrenesulfonate and 2.45 g (34.0 mmol) of acrylic acid were used. A lithium ion secondary battery was manufactured. In the copolymer solution of Comparative Example 2, the molar ratio of the styrene sulfonic acid monomer unit to the acrylic acid monomer unit is 3: 7.

(Comparative Example 3)
1 g (4.9 mmol) of sodium styrenesulfonate and 3.15 g (43.7 mmol) of acrylic acid were dissolved in 20 g of water to obtain an aqueous solution. Under a nitrogen atmosphere, 30 mg of ammonium persulfate was added to the aqueous solution, and then the temperature of the aqueous solution was heated to 60 ° C. under stirring conditions to initiate the copolymerization reaction. Thereafter, a copolymer solution, a polymer layer, a negative electrode, and a lithium ion secondary battery of Comparative Example 3 were produced in the same manner as in Example 1. In the copolymer solution of Comparative Example 3, the molar ratio of the styrene sulfonic acid monomer unit to the acrylic acid monomer unit is 1: 9.

(Comparative Example 4)
2.45 g (34.0 mmol) of acrylic acid was dissolved in 10 g of water to make an aqueous solution. Under a nitrogen atmosphere, 30 mg of ammonium persulfate was added to the aqueous solution, and then the temperature of the aqueous solution was heated to 60 ° C. under stirring conditions to initiate the polymerization reaction. Hereinafter, the polymer solution, polymer layer, negative electrode, and lithium ion secondary battery of Comparative Example 4 were produced in the same manner as in Example 1. In the polymer solution of Comparative Example 4, the molar ratio of the styrene sulfonic acid monomer unit to the acrylic acid monomer unit is 0:10.

(Comparative Example 5)
2.45 g (34.0 mmol) of acrylic acid was dissolved in 10 g of water to make an aqueous solution. Under a nitrogen atmosphere, 30 mg of ammonium persulfate was added to the aqueous solution, and then the temperature of the aqueous solution was heated to 60 ° C. under stirring conditions to initiate the polymerization reaction. After the reaction solution was stirred at 60 ° C. for 5 hours, the reaction solution was cooled to room temperature, 0.107 g of a 10 mass% sodium hydroxide aqueous solution was added, and the mixture was stirred for 30 minutes. The polymer solution after stirring was used as the polymer solution of Comparative Example 5.
Thereafter, the polymer layer, the negative electrode, and the lithium ion secondary battery of Comparative Example 5 were produced in the same manner as in Example 1. In the polymer solution of Comparative Example 5, the molar ratio of the styrene sulfonic acid monomer unit to the acrylic acid monomer unit is 0:10, and the acrylic acid monomer unit is sodium acrylate.

(Comparative Example 6)
A lithium ion secondary battery of Comparative Example 6 was produced in the same manner as in Example 1, except that the negative electrode precursor of Example 1 that was not coated with the polymer layer was used as the negative electrode.

(Evaluation Example 1: Ionic conductivity)
With respect to the polymer layers of Examples 1 to 3 and Comparative Examples 1 to 5, the ionic conductivity was measured using a complex alternating current impedance measuring device. The results are shown in Table 1. The molar ratio in Table 1 and the subsequent tables means the molar ratio of styrene sulfonic acid monomer units to acrylic acid monomer units. The acrylic acid monomer unit of Comparative Example 5 is sodium acrylate.

  From Table 1, it can be seen that the polymer layer of each example showed excellent ionic conductivity as compared with the polymer layer of each comparative example. In particular, it can be said that the ionic conductivity of the polymer layer of Example 1 is remarkably high.

(Evaluation Example 2: Infrared absorption spectrum)
The infrared absorption spectrum of the polymer layer of Example 1 was measured using an infrared spectrophotometer. From the polymer layer of Example 1, peaks derived from styrene sulfonic acid monomer units and acrylic acid monomer units were clearly observed.

(Evaluation example 3: battery evaluation)
The lithium ion secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 6 were charged to 0.01 V at a current of 0.05 C rate, and then 1. Discharge was performed to 0V. From the charge capacity and discharge capacity values observed in this charge / discharge, the initial efficiency was calculated by the following equation.
Initial efficiency (%) = 100 × (discharge capacity) / (charge capacity)
Further, with respect to the lithium ion secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 6, the battery was charged to 0.01 V at a current of 0.05 C rate, and thereafter, at a current of 0.5 C rate. The battery was discharged to 1.0 V, and the discharge capacity was measured. A value obtained by dividing the discharge capacity by the discharge capacity when the initial efficiency was calculated was calculated as a rate characteristic. Here, the rate characteristic is a parameter comparing the discharge capacities when the discharge currents differ by 10 times.
Further, the lithium ion secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 6 were charged to 0.01 V at a constant current of 0.3 C rate, and thereafter, constant current of 0.3 C rate. The charge / discharge cycle of discharging to 1.0 V was repeated 20 times. The capacity retention rate was calculated according to the following formula.
Capacity maintenance rate (%) = 100 × (discharge capacity at 20th cycle) / (discharge capacity at 1st cycle)
The results are shown in Table 2.

  From the results in Table 2, it can be seen that the lithium ion secondary batteries of the examples showed results equal to or higher than those of the comparative example in all evaluation items of initial efficiency, rate characteristics, and capacity retention rate. On the other hand, the lithium ion secondary batteries of Comparative Example 1 and Comparative Example 6 have a significantly lower capacity retention rate than other lithium ion secondary batteries. The lithium ion secondary batteries of Comparative Examples 2 to 5 have lower initial efficiency and rate characteristics than the lithium ion secondary batteries of the examples.

  From the results in Table 1 and Table 2, the molar ratio of the styrene sulfonic acid monomer unit to the (meth) acrylic acid monomer unit is in the range of 9.5: 0.5 to 7: 3. The polymer layer has good ionic conductivity, and the secondary battery of the present invention having the polymer layer of the present invention can be said to have excellent battery characteristics. From the results of the capacity retention rate, it can be said that the polymer layer of the present invention was able to follow the expansion and contraction of the silicon material accompanying charge / discharge.

(Example 4)
6 g (29.1 mmol) of sodium styrenesulfonate and 0.233 g (3.2 mmol) of acrylic acid were dissolved in 30 g of water to obtain an aqueous solution. Under a nitrogen atmosphere, 30 mg of ammonium persulfate was added to the aqueous solution, and then the temperature of the aqueous solution was heated to 60 ° C. under stirring conditions to initiate the copolymerization reaction. After the reaction solution was stirred at 60 ° C. for 5 hours, the reaction solution was cooled to room temperature, 1.28 g of a 10 mass% sodium hydroxide aqueous solution was added, and the mixture was stirred for 30 minutes. The copolymer solution after stirring was used as the copolymer solution of Example 4.
Hereinafter, the polymer layer, negative electrode, and lithium ion secondary battery of Example 4 were produced in the same manner as in Example 1. In the copolymer solution of Example 4, the molar ratio of the styrene sulfonic acid monomer unit to the acrylic acid monomer unit is 9: 1, and the acrylic acid monomer unit is sodium acrylate.

(Example 5)
6 g (29.1 mmol) of sodium styrenesulfonate and 0.170 g (3.2 mmol) of acrylonitrile were dissolved in 30 g of water to obtain an aqueous solution. Under a nitrogen atmosphere, 30 mg of ammonium persulfate was added to the aqueous solution, and then the temperature of the aqueous solution was heated to 60 ° C. under stirring conditions to initiate the copolymerization reaction. After stirring the reaction solution at 60 ° C. for 5 hours, the reaction solution was cooled to room temperature and stirred for 30 minutes. The copolymer solution after stirring was used as the copolymer solution of Example 5.
Thereafter, the polymer layer, negative electrode, and lithium ion secondary battery of Example 5 were produced in the same manner as in Example 1. In the copolymer solution of Example 5, the molar ratio of the styrene sulfonic acid monomer unit to the acrylic acid monomer unit is 9: 1, and the acrylic acid monomer unit is acrylonitrile.

(Example 6)
6 g (29.1 mmol) of sodium styrenesulfonate and 0.230 g (3.2 mmol) of acrylamide were dissolved in 30 g of water to obtain an aqueous solution. Under a nitrogen atmosphere, 30 mg of ammonium persulfate was added to the aqueous solution, and then the temperature of the aqueous solution was heated to 60 ° C. under stirring conditions to initiate the copolymerization reaction. After stirring the reaction solution at 60 ° C. for 5 hours, the reaction solution was cooled to room temperature and stirred for 30 minutes. The copolymer solution after stirring was used as the copolymer solution of Example 6.
Hereinafter, the polymer layer, negative electrode, and lithium ion secondary battery of Example 6 were produced in the same manner as in Example 1. In the copolymer solution of Example 6, the molar ratio of the styrene sulfonic acid monomer unit to the acrylic acid monomer unit is 9: 1, and the acrylic acid monomer unit is acrylamide.

(Example 7)
3 g (14.6 mmol) of sodium styrenesulfonate and 0.186 g (1.6 mmol) of 2-hydroxyethyl acrylate were dissolved in 150 g of water to obtain an aqueous solution. Under a nitrogen atmosphere, 30 mg of ammonium persulfate was added to the aqueous solution, and then the temperature of the aqueous solution was heated to 60 ° C. under stirring conditions to initiate the copolymerization reaction. After stirring the reaction solution at 60 ° C. for 5 hours, the reaction solution was cooled to room temperature and stirred for 30 minutes. The copolymer solution after stirring was used as the copolymer solution of Example 7.
Hereinafter, the polymer layer, negative electrode, and lithium ion secondary battery of Example 7 were produced in the same manner as in Example 1. In the copolymer solution of Example 7, the molar ratio of the styrene sulfonic acid monomer unit to the acrylic acid monomer unit is 9: 1, and the acrylic acid monomer unit is 2-hydroxyethyl acrylate.

(Evaluation Example 4: Ionic conductivity and battery evaluation)
With respect to the polymer layers of Examples 4 to 7, ion conductivity was measured in the same manner as in Evaluation Example 1. Furthermore, battery evaluation was performed on the lithium ion secondary batteries of Examples 4 to 7 in the same manner as in Evaluation Example 3. Together with the results of Example 1, the above results are shown in Tables 3 and 4.

  From the results of Table 3, it can be said that the preferable order of acrylic monomer units is acrylamide, sodium acrylate, acrylic acid, acrylonitrile, and 2-hydroxyethyl acrylate from the viewpoint of ion conductivity.

  Moreover, even if it has any kind of acrylic acid type monomer unit from the result of Table 4, it turns out that the lithium ion secondary battery of the Example showed the outstanding battery characteristic. From the standpoint of initial efficiency and rate characteristics, the lithium ion secondary batteries of any of the examples are equivalent, and from the point of capacity maintenance rate, the lithium ion secondary batteries of Examples 1, 4 and 5 Is particularly good.

Claims (6)

An electrode for a secondary battery coated with a polymer layer containing a copolymer of styrenesulfonic acid or a salt thereof and a (meth) acrylic acid monomer,
An electrode for a secondary battery, wherein a molar ratio of a styrene sulfonic acid monomer unit to a (meth) acrylic acid monomer unit in the polymer layer is in a range of 9.5: 0.5 to 7: 3.   The said (meth) acrylic-acid type monomer is selected from (meth) acrylic acid, (meth) acrylate, (meth) acrylonitrile, (meth) acrylamide and (meth) acrylic acid ester. Secondary battery electrode.   The said secondary battery electrode is equipped with the electrical power collector, the negative electrode active material layer formed on the said electrical power collector, and the said polymer layer which coat | covers the said negative electrode active material layer. Secondary battery electrode.   The secondary battery electrode according to claim 3, wherein the negative electrode active material layer includes a silicon material having a structure in which a plurality of plate-like silicon bodies are laminated in a thickness direction.   The electrode for a secondary battery according to any one of claims 1 to 4, wherein the polymer layer has a thickness of 0.5 to 10 µm.   The secondary battery which comprises the electrode for secondary batteries of any one of Claims 1-5.

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